The present application is related to and claims the priority of Korean Application No. PATENT-2001-0057560 filed Sep. 18, 2001, in the name of Young Woo PARK, and titled COMPACT ZOOM LENS and Korean Application No. PATENT-2002-0025599 filed May 9, 2002, in the name of Young Woo PARK, and titled COMPACT ZOOM LENS, the entire contents of which are fully incorporated herein by reference.
This invention relates generally to a compact zoom lens system used in a camera with a pick-up device such as a charge coupled device (CCD).
Popularization of electronic still cameras and video cameras with charge coupled device or solid-state pickup device has recently spread as they have become lighter in weight and lower in cost. Accordingly, demand is growing for a zoom lens system built into cameras with the pick-up device that has light weight and low cost.
An optical system used in a camera with a pick-up device utilizes a crystal filter to prevent the moirxc3xa9 effect. This effect occurs as a result of the periodic structure of the pick-up device. Consequently, the thickness and the position of the crystal filter must be considered when designing an optical system. Additionally, the telecentricity of rays of light inputted to an image plane becomes an important design parameter.
Zoom lens systems used in a camera with a pick-up device are disclosed in Japanese Publication Nos. Sho 56-123512, Hei 6-94996, Sho 63-292106, and Hei 5-173071. The zoom lens system of Japanese Publication No. Sho 56-123512 includes, when viewed from an object, a first lens group of negative refractive power and a second lens group of positive refractive power. The second lens group moves to vary the magnification of the zoom lens system. The first lens group moves to compensate the movement of an image point due to the variation of the magnification. However, when zooming the first and second lens groups move along an optical axis. Subsequently, as magnification changes, the total length of the zoom lens system increases. This results in the complex barrel structure. It also increases difficulty of achieving a zoom ratio or magnification ratio of over 2. Finally, it makes difficult to create a compact zoom lens system.
The zoom lens system of Japanese Publication No. Hei 6-94996 includes three lens groups. To compensate for various kinds of aberration occurring due to the variation in magnification, a third lens group of a negative or positive refractive power is located on the side of a second lens group facing an image. As a result, a magnification ratio increases and the size of the zoom lens system remains compact. When zooming, the first and second lens groups move along an optical axis to vary the magnification, and the third lens group stays fixed. However, the total length of the zoom lens system varies, and the magnification ratio does not exceed 2.0.
The zoom lens system of Japanese Publication No. Sho 63-292106 is an optical system in which the total length of the zoom lens system does not vary during zooming. The optical system includes a first lens group which is fixed during the zooming and which has a negative refractive power, a second lens group of a positive refractive power, and a third lens group of a positive refractive power. The second and third lens groups move axially when zooming. However, since the second and the third lens groups move toward an object when zooming, a problem arises. More specifically, the total length of the zoom lens system should be large enough to compensate optical performance of the zoom lens system at a wide-angle position. As a result, the size of the zoom lens system increases, and thereby makes it difficult to build a compact zoom lens system.
The zoom lens system of Japanese Publication No. Hei 5-173071 includes, when viewed from an object, a first lens group of a negative refractive power, a second lens group of a positive refractive power, a third lens group of a positive refractive power, and a fourth lens group of a positive refractive power. However, since all the lens groups move when zooming, this structure results in the complex barrel structure.
It is therefore desirable to provide a compact zoom lens system that has a high magnification ratio with a simple construction of the optical system and which may be used in a camera with a pick-up device. It is also desirable to provide a zoom lens system that has good optical performance due to well compensating chromatic aberrations.
There is provided a compact zoom lens system, when viewed from an object side, comprising a first lens group of a negative refractive power, the first lens group comprising at least one lens of a negative refractive power and one lens of a positive refractive power; a second lens group of a positive refractive power, the second lens group comprising a first lens of a positive refractive power, a second lens of a positive refractive power, and a third lens of a negative refractive power; and a third lens group of a positive refractive power, the third lens group comprising at least a lens of a positive refractive power, wherein the first, the second, and the third lens groups move along an optical axis. The zoom lens system satisfies the following conditions:       0.4    ≤                  t        II                                          f            W                    ⁢                      f            T                                ≤          0.6      ⁢              xe2x80x83            ⁢      and      ⁢              xe2x80x83            ⁢      2.8        ≤                  f        T                    f        W              ≤    3.0    ,
wherein
fW represents a total focal length at a wide-angle position;
fT represents a total focal length at a telephoto position; and
tII represents a total thickness of the second lens group.
The zoom lens system further satisfies the following conditions:       1    ≤                  L        II                                          f            W                    ⁢                      f            T                                ≤          1.5      ⁢              xe2x80x83            ⁢      and      ⁢              xe2x80x83            ⁢      1.7        ≤                  f        III                                          f            W                    ⁢                      f            T                                ≤    3    ,
wherein
fIII represents a focal length of the third lens group; and
LII represents an amount the second lens group moves from the wide-angle position to the telephoto position. Also, the zoom lens system further satisfies the following condition:       0.4    ≤          "LeftBracketingBar"                        f                      I            ⁡                          (              -              )                                                f                      I            ⁡                          (              +              )                                          "RightBracketingBar"        ≤    0.6    ,
wherein
fI(xe2x88x92) represents a focal length of a lens which has a negative refractive power in the first lens group; and
fI(+) represents a focal length of a lens which has a positive refractive power in the first lens group.
There is also provided a compact zoom lens system, when viewed from an object side, comprising a first lens group of a negative refractive power; a second lens group of a positive refractive power, the second lens group comprising a first lens of a positive refractive power, a second lens of a positive refractive power, and a third lens of a negative refractive power, wherein two lenses among the first lens, the second lens and, the third lens are cemented; and a third lens group of a positive refractive power, wherein the first, the second, and the third lens groups move along an optical axis when zooming from a wide-angle position to a telephoto position. The zoom lens system satisfies the following conditions:       0.8    ≤                  D        IIW                    f        W              ≤          1.2      ⁢              xe2x80x83            ⁢      and      ⁢              xe2x80x83            ⁢      0.4        ≤                  t        II                                          f            W                    ⁢                      f            T                                ≤    0.6    ,
wherein
DIIW represents a distance between the second lens group and the third lens group at the wide-angle position.
There is also provided a compact zoom lens system, when viewed from an object side, comprising a first lens group of a negative refractive power; a second lens group of a positive refractive power, the second lens group comprising a first lens of a positive refractive power, a second lens of a positive refractive power, and a third lens of a negative refractive power; and a third lens group of a positive refractive power, wherein the first, the second, and the third lens groups move along an optical axis when zooming from a wide-angle position to a telephoto position. The zoom lens system satisfies the following conditions:             -      0.2        ≤                  L        III                                          f            W                    ⁢                      f            T                                ≤    0.1    ,            and      ⁢              xe2x80x83            ⁢      0.8        ≤                  D        IIW                    f        W              ≤    1.2    ,            and      ⁢              xe2x80x83            ⁢      0.4        ≤                  t        II                                          f            W                    ⁢                      f            T                                ≤    0.6    ,
wherein
LIII represents an amount the third lens group moves from the wide-angle position to the telephoto position.
The zoom lens systems further satisfies the following condition:
0.25xe2x89xa6|nII1xe2x88x92nII2|xe2x89xa60.4,
wherein
nII1 represents a refractive index of the first positive lens in the second lens group; and
nII2 represents a refractive index of the second positive lens in the second lens group.
In the zoom lens systems, the third lens group may comprise one lens of a positive refractive power. The first lens group and the second lens group may comprise at least one aspherical surface and two lenses among the first lens, the second lens, and the third lens of the second lens group may be cemented.
Additional features and advantages will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the claims. The advantages will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the appended claims.